Process for modifying wood pulp for rapid dispersion



Patented Aug. 5, 1952 UNITED STATES PATENT OFFICE 2,606,115 Y PRooEss FOR MODIFYING WOOD PULP FOR RAPID DISPERSION 1 Albert C. Nuessle, Lyndalia, and Williiam P. Hall, Wilmington, Del., assignors to Joseph Bancroft & Sons (30., Wilmington, Del., a corporation of Delaware No Drawing. Application March 23, 1946, Serial No. 656,778

6 Claims. 1

When cellulose fibers are closely packed together such as, for example, in wood pulp sheets used in the manufacture of cellulose products, the dispersion of the pulp sheets into their individual fibers is a difiicult job and requires the use of complex beating machinery, and even then the results are not uniformly satisfactory.

This invention relates to a simple and effective method of dispersing said wood pulp into its individual fibers in water without mechanical agitation, and this method may in addition impart flame-resistant, glow-resistant and mildewresistant properties to the fibers.

Generally considered, we apply to the pulp sheets an aqueous solution of a strong acid, such as orthophosphoric acid, and an organic nitrogen containing base, such as urea, dry the impregnated pulp in a conventional manner to remove substantially all of the moisture, and then cure by applying heat at a temperature and for a time sufiicient to bring about a chemical combination between the chemicals and the cellulose whereby acid groupings and nitrogen groupings are contained in the complex of cellulose, acid and nitrogen.

The impregnated and cured pulp sheets have the same physical appearance as the original sheets but when immersed'in hot water the individual fibers immediately separate and form a cloud-like dispersion in the water. This fine dispersion may be used in the production of cellulose products such as, for example, paper.

The fibers by virtue of the presence of acid and nitrogen groupings, are rendered substantially flame-resistant, glow-resistant and mildew-resistant, these properties being, for all practical purposes, of a durable character toward water and organic solvents.

The physical characteristics of the fibers, such as strength, are largely retained as compared with the original state.

The chemical solution is prepared by mixing together, either with or without the application of heat, the nitrogen containing compounds and the acid or acids. Water is preferably used to form a substantially clear solution.

Since the acid combines with the cellulose during curing, we prefer to use strong acids which are neither excessively volatile nor produce chemicals which will detrimentally alter the physical characteristics of the fibers under the conditions of the process; such acids, for example, as orthophosphoric acid, pyrophosphoric acid, sulfuric acid, polyphosphoric, orthophosphorous, pyrophosphorous and metaphosphoric acids,

salts of said acids, substitution products of said acids, and anhydrides of said acids.

The anhydrides', salts and substitution products of the acids should be capable of producing the proper acid conditions during curing to insure combination with the cellulose. Volatile salts such as ammonium salts and mono-substituted poly-acids are therefore recommended as these products would produce the proper conditions during curing for the combination with the cellulose.

Among substituted acids we may mention, for example, phosphamic, sulphamic, chlorosulphonic, dinitride hexaphosphoric, diamido phosphoric, monosodium orthophosphoric and phenyl phosphoric acid. The presence of metallic elements attached to the acid tend to reduce the dispersion tendency; thus, for example, orthophosphoric acid and urea give excellent dispersion, monosodium orthophosphate and urea give moderate dispersion and disodium phosphate and urea negligible dispersion.

Organic substituted groups on the acid or on the nitrogen compound also tend to reduce the dispersion tendency, for example, phenyl phosphonic acid gives only moderate dispersion and the use of ethylurea instead of urea also reduces the dispersion tendency.

It is possible by the methods described, for some purposes to combine other acids with the cellulose such as, for example, phthalic, glutaric, selenic, telluric and pyroantimonic. The dispersion obtained with these acids is, however, small by comparison, and we prefer to use the strong acids listed above. Uniformly excellent results have been obtained with sulfuric and orthophosphoric acids which are inexpensive and easily available, and we recommend these acids as the most practical in large scale production.

Since the acids are strong in nature, it is necessary to introduce a buffering agent into the mixture. For this purpose, we prefer to use urea which has an'afiinity for the acids and will compete with the cellulose for the acid during ouring, and thus prevent undesirable alteration in the cellulose. The urea is used in substantial excess and'part of it removed during the subsequent washing of the dispersed pulp. Part of it becomes a durable part of the cellulose-acid complex, as can be shown by the presence of nitrogen in the washed and dried pulp. It may be used in excess because changes in quantity employed do not strongly affect pH.

Other weak nitrogen-containing bases may be sed, to replace part of the urea and satisfactory buiiering action obtained, but under these circumstances the rate and degree of dispersion of the pulp when immersed in hot water are correspondingly reduced, the most satisfactory dispersion being obtained by the use of urea. Among the weak nitrogen bases we may mention, for example, biuret, formamide, acetamide, ethylurea, dibutyl urea, hydroxyethyl-urea, dicyandiamide and cyanoacetamide.

In some cases, where the solubility of the weak.

base is not high even in hot solution, it becomes undesirable to use said base alone since the desired excess of this materialmay create ansubstantially reduces the acidic. properties of the acid. Furthermore, the strong bases correspondingly affect pH, a moderate change in amount efiecting a substantial changein pH. The use of bases containing metals should in general be avoided as they tend to decrease the dispersion as will be further described.

The pH of the solution itself is of no importance but the pH of the cured pulp is important. To obtain the proper reaction with the cellulose, the pH on the cured pulp should be from about 2 to about 7, the preferred range being from about 3 to about 6, the measurements being made by indicator solutions on the cured pulp. Below these limits excess degradation of the cellulose takes place and above these limits the combination becomes negligible. The pH of the solution may be higher; so long as the pH on the cured pulp comes down to the values indicated. Ordinarily, a solution pH, pH higher gives good results, although it may be even higher.

The solution may be applied in any conventional way such as dipping, spraying, padding and the like. We prefer steeping the cellulose material in the solution until thoroughly impregnated and then squeezing out the excess solution, leaving enough chemicals on the ma-- terial to insure good disperson, as will be further described.

The concentration. of the solution itself is unimportant since successive impregnations, with alternate dryings, permit the addition of the required quantity of material.

The impregnated pulp is now dried to remove substantially all of the moisture, and is then cured to allow the required reactions to take place. The drying and curing may conveniently be combined into one operation.

The time and temperature of curing. are very important in obtaining maximum dispersion, and are dependent upon a number of factors such as, for example, solution chemicals used, quantity of chemicals on pulp, pH of cured pulp, type and physical shape of pulp sheet and so forth. However, if these factors remain constant, a definite time and. temperature relation exists when good dispersion is obtained. For example, using urea, guanidine carbonate, and orthophcsphoric acid on hemlock wood pulp sheets, it was found that curing at 320 F. for 5 minutes gave moderate dispersion, curing at 320 F. for 8 minutes gave excellent dispersion, curing at 820 F. for 11 minutes gave moderate disper- 4 sion, and curing at 320 F. for 14 minutes gave practically no dispersion.

In general, we :may operate between 250 F. and 400 F., the preferred range being 300 F. to 350. F. The time varies inversely with the temperature, other conditions remaining the same. For the preferred range of temperatures, we may use from about 2 minutes to about 30 minutes, the most desirable range being from 3 minutes to 15 minutes. Beyond these temperatures and time limits results may be obtained, but the processbecomes either commercially impracticalv or. difficult to control. For temperatures of approximately 250 F., the time required is approximately 180 minutes, and at 400 F., approximately 1 minute.

The quantity of chemicals on the cured pulp is also important, other factors remaining the same. With large volumes of dispersion medium, the greater the quantity of chemicals, the greater and more rapid the dispersion up until a certain point, where additional chemicals do not seem to change the degree and rapidity of dispersion to any great extent. For example, excellent dispersion was obtained in hot water when wood pulp sheets were treated as above described, using a urea-orthophosphoric acid solution containing 50% urea and 19% orthophosphoric acid and with a solution pick-up of 162% by Weight. This represents a solid chemical pick-up by the pulp of about 111% by weight, with a chemical or solids add-on by the cured pulp of about 81%, and an ultimate chemical add-on by the cured and Washed pulp of 19%. When the solution concentration was changed to 8% urea and 4.5% acid and the same pick-up used, representing a solid chemical pick-up of about 20%, and an add-on by the cured pulp of about 15%, and an ultimate add-on on. the cured and washed pulp of about 5%,, the dispersion was moderate. When 3% urea and 1.5% acid was used with 162% pick-up, representing a solid chemical pick-up of about 7.3% and a chemical add-on of the cured pulp of about 5.5%, and an ultimate add-on of the cured and washed pulp of about 1.8%, the dispersion was negligible. The excess chemicals, removed by the subsequent washing, play an important part in the dispersion effect. This can be seen from the fact that pulp once dispersed and then washed with Water to remove excess chemical and dried, will disperse only slightly or not at all when again immersed in hot water.

The solid chemical add-on by the impregnated and dried pulp may vary between 8% to about 110% by weight, the solid chemical add-on on the cured pulp may vary from 5% to about and the ultimate solid chemical add-on of the cured and washed pulp may vary from 2% to about 20% by weight and representing an excess of uncombined chemicals on the cured pulp of from about 6% to about using urea and orthophosphoric acid by way of illustration. From what has been said, better results are obtained when operating above the low limits given. In the case of orthophosphoric acid and urea, the phosphorous in the cured and washed pulp may range from about /2% to about 6%, and nitrogen from about 4% to about by way of illustration.

The relative percentages of phosphorous and nitrogen on the cured and washed fibers may be changed by changing the ingredients, for example, by changing the nitrogen compounds in the above formula from urea to a mixture of urea, dicyandiamide and guanidine, the percentage of nitrogen in the solid add-on may be substantially increased. (We prefer that the ratio of base to acid in the impregnating solution shall be on the order, roughly, of 2 to l. The ratio, however, may vary quite widely.)

The solid chemical add-on may be increased to a large quantity by, for example, immersing the pulp in a molten mixture of urea and orthophosphoric acid and removing the pulp without squeezing out the excess, but such great excess serves no further improvement and may slow and decrease the dispersion in case the volume of water used for the dispersion is small.

The condition of the pulp before dispersion has some effect. For example, a hot dry pulp will disperse more quickly than a cold damp pulp, other conditions being the same. Y

The dispersion medium is of great importance and should preferably be used in large excess and at elevated temperatures to obtain a complete and rapid dispersion of the fibers. Pure water is the best dispersion medium and any addition of soluble chemicals to the water, whether acids, bases or salts, tend to reduce the ease with which the fibers disperse and if used in excess these materials may practically completely prevent the dispersion. For example, pulp previously treated as described with urea and orthophosphoric, when immersed in an excess of a .4%' sodium hydroxide solution, gives approximately the same dispersion as in water, but when immersed in an excess of a solution of sodium hydroxide practically no dispersion takes place.

The different acids, bases and salts which may be present in the dispersion medium may vary in the degree with which they retard the dispersion but in all cases the retarding action is increased with increasing concentration. It is therefore evident that with a large excess of chemicals on the pulp, sufficient water should be used in the dispersion of the pulp to prevent the formation of a concentrated solution which would retard the dispersion. v r

Some dispersion may be obtained even in concentrated chemical solutions by heating to high temperatures, especially to the boiling point, where the mechanical agitation provided by the boiling solution favors the dispersion. For example, properly treated pulp may be dispersed in boiling 75% orthophosphoric acid (250 F.).

Water soluble organic solvents tend to decrease the dispersion when added to the water dispersion medium. Pure organic solvents do not give dispersion, although some dispersion takes place in highly polar materials, such as, for example, molten urea or molten dicyandiamide.

An increase in the temperature of the water used for dispersion increases the rate and degree of the pulp dispersion, maximum results being obtained in boiling water. Thedispersion in cold Water may be increased by using hot dry pulp.

This process is applicable to all types of cellulose fibers where these fibers are closely packed together without a binding material, and is especially adapted to short fibers, such as occur in WOOd.

The pulp dispersion obtained may be used in further processing such asin the manufacture of paper. Other ingredients may be added such as fillers, binders and so forth; this, however, forms no part of this invention.

To further illustrate the invention without placing limitations thereupon, the following ex- 6 amples are given. All ingredient quantities are given by weight.

Example I Hemlock wood pulp sheets were immersed 2 minutes in a solution comprising:

- 200 parts urea parts orthophosphoric acid (75%) 100 parts water Ewainple II Pine wood pulp sheets were immersed 2 minutes in a solution comprising; 200 parts urea I 100 parts sulfuric acid 200 parts water and then squeezed to remove excess solution (approximately 180% solution pick-up). The sheets were then dried and cured 4 minutes at 320 F.

The sheet, when immersed; in hot water as above, dispersed immediately into its individual fibers. These, after washing in water, were found to be flame, glow and mildew-resistant.

Example III Tightly compressed combed pure cotton was impregnated with a solution comprising:

200 parts urea 100 parts ammonium-dihydrogen-phosphate 200 parts water The excess solution was removed by squeezing (approximately solution pick-up) and the fibers then dried and cured 7 minutes at 340 F.

When immersed in hot water the fibers dispersed. The fibers after washing were found to be flame, glow and mildew-resistant.

v Example IV Pine wood pulp sheets were immersed in a mixture comprising:

100 parts urea 48 parts sulphamic acid 48 parts water Ewample V.

Hemlock wood pulp sheets were immersed in a mixture comprising: V

500 parts urea 500 parts acetamide 500 parts orthophosphoric acid (75 500 parts water flame, glow and mildew-resistant.

Hemlock wood pulp, treated as described in Example I, was immersed in hot water and the dispersed fibers washed to remove excess chemicals. To the dispersed fibrous. material was added a small quantity of ammonium rosinate as a binder, and the resulting mixture put in a Fourdrinier screen to remove water and dry.

The sheet of paper obtained was calendered, and

when tested, was found to be flame-resistant, glow-resistant and mildew-resistant.

Example VII Hemlock wood pulp sheets were, impregnate with the following solution:

200 parts urea 100 parts water 100 parts orthophosphoric acid ('7 400 total of which 275 parts, or 69%, are solid matter. The pulp was then squeezed, dried, cured, dispersed and redried.

Weight of dispersed,

washed dried pulp 31 parts or 19% add-on Loss on curing: 1l1%- 8l% or 30/111=27% loss (of total solids) Loss on washing: 31 19% or 62/111=56% loss (of total solids) Remaining 19% is the chemical-fixed solids.

Per cent available acid which combined: '75H3PO4/400 total solutionx 162% wet pickup=30% H3PQ4 available on pulp.

Actually about 19% combined. Thus 13/30:

roughly 68% of available acid combined.

Example, VIII Hemlock wood pulp was impregnated at 180 F. with a, mixture of 258 parts biuret 200 parts water 100 parts orthophosphoric acid (75 followed by squeezing and drying.v The mixture pick-up was 150% by weight.

The pulp was cured and then dispersed in an excess of. water at 160 F. and the following results obtained:

Cured l min. 320 F.-no dispersion Cured 2 min. 320 F.'slig ht dispersion Cured 4 min. 320 F.rapid dispersion Cured 8 min. 320 l te-slight dispersion Cured 12min. 320 F.-n o dispersion Example IX Hemlock wood pulp sheets were impregnated with a mixture of:

500 parts urea 500 parts water 120 parts fiuorosulphonic acid squeezed to give 150% pick-up and then dried. One-half of thetreated pulp was cured at 400 F. and the other half at 250 F. andthen dispersed in hot water. Thefollowing results were obtained:-

Cured /2 minute at 400 F.neg1igib1e dispersion. Cured 1 minute at 400 F,s1ight dispersion Cured 2 minutes at 400 F.-rapid dispersion Cured 4 minutes at 400 F.slight dispersion Cured. minutes at 250 E.slight dispersion Cured 60 minutes at 250 F.-moderate dispersion Cured 90 minutes at 250 F.rapid dispersion Cured 120 minutes at 250 F.-moderate disper- S1011 Cured 150 minutes at 250 F.moderate disper-.

sion

Example X Hemlock wood pulp sheets were immersed in the following solution:

150 parts urea 60 parts guanidine carbonate 80 parts phosphoric acid (75%) 210 parts water squeezed as. before and dried. Samples of this pulp were then cured as follows:

25 Samples Time Temp.

M inutcs F 1 2 320 5 320 8 320 11 320 14 320 When immersed inhot water the following derees of dispersionwere obtained:

Sample 1.-Poor Sample 2.Moderate Sample Zia-Excellent Sample 4.Moderate Sample 5.Poor.

It will be seen from what has heretofore been said that for a given temperature, there is a critical time at which maximum dispersion effeet is obtained, the time-dispersion eifect curve rising to a peak (the critical time) and then falling off as the time of treatment is continued. It is obvious that to obtain the maximum dispersion efiect the curing should be continued until the critical time point is arrived at. This may vary somewhat, depending upon the acid used, etc., but in each case, for a given temperature, the critical time point can be readily ascertained by test.

We claim:

1. The process of dispersing closely packed cellulose fibers in the form of sheets, blocks and the like, which consists in applying to the compacted fibers an aqueous solution containing (1) at least one acidic agent having a base element selected from the class which consists of sulphur and phosphorus, namely: orthophosphoric, metaphosphoric, pyrophosphoric, polyphosphoric, orthophosphorous, pyrophosphorous, phosphamic, dinitride hexaphosphoric, diamido phosphoric, monosodium orthophosphoric, and phenyl phosphoric acids, sulphuric, sulphamic, clorosulphonic and fluorosulphonic acids, sulphuric anhydride, and phosphorous anhydride, and (2) at least one non-metallic nitrogen-containing organic compound basic with respect to the acidic agent in the solution, selected from the class which consists of urea, biuret, formamide, acetamide, ethylurea, dibutyl-urea, hydroxyethyl-urea, dicyandiamide, cyanoacetamide, guanidine, guanyl urea, and biguanide, the amount of solidsapplied ranging from 8% to 110% by weight of the pulp in the dry state, and the ratio of acidic and basic constituents in said solution being such as to yield a product which, after the baking to be hereinafter defined, has a, pH of from 2 pH to 7 pH as determined by indicator solutions, and contains an amount of combined base element of the acid which is the efiective equivalent of from /2% to 6% of phosphorous, and an amount of combined nitrogen from 4% to 0.25% by weight; thereafter drying the fibers; subsequently reacting the acidic constituent, the nitrogenous basic constituent and the cellulose by baking the fibers at temperatures between 250 F. and 400 F. for a time ranging from 180 minutes at the lower temperature to 1 minute at the higher temperature so as to produce a complex containing the acid, cellulose and nitrogen; and subsequently immersing the baked fibers, still in compacted form, in hot water, whereby to effect rapid and substantially complete dispersion of the fibrous material throughout the body of water.

2. The process of claim 1 in which the acid is orthophosphoric.

3. The process of claim 1 in which the acid is orthophosphoric and the nitrogen containing compound is urea.

4. The process of claim 1 in which the nitrogen containing compound is urea.

5. The process of claim 1 in which the acid is sulfuric.

6. The process of claim 1 in which the acid is sulfuric and the nitrogen containing compound 15 urea.

' ALBERT C. NUESSLE.

WILLIAM P. HALL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,953,832 Sandell Apr. 3, 1934 2,089,697 Groebe Aug. 10, 1937 2,212,152 Cupery Aug. 20, 1940 2,233,475 Dreyfus Mar. 4, 1941 2,286,726 Gordon June 16, 1942 2,401,440 Thomas June 4, 1946 OTHER REFERENCES Hackhs Chemical Dictionary, 3rd ed. (1944). pp. 146 and 315. 

1. THE PROCESS OF DISPERSING CLOSELY PACKED CELLULOSE FIBERS IN THE FORM OF SHEETS, BLOCKS AND THE-LIKE, WHICH CONSISTS IN APPLYING TO THE COMPACTED FIBERS AN AQUEOUS SOLUTION CONTAINING (1) AT LEAST ONE ACIDIC AGENT HAVING A BASE ELEMENT SELECTED FROM THE CLASS WHICH CONSISTS OF SULPHUR AND PHOSPHORUS, NAMELY; ORTHOPHOSPHORIC, METAPHOSPHORIC, PROPHOSPHORIC, POLYPHOSPHORIC, ORTHOPHOSPHOROUS, PYROPHOSPHOROUS, PHOSPHAMIC, DINITRIDE HEXAPHOSPHORIC, DIAMIDO PHOSPHORIC, MONOSODIUM ORTHOPHOSPHORIC, AND PHENYL PHOSPHORIC ACIDS, SULPHURIC, SULPHAMIC, CHLOROSULPHONIC AND FLUOROSULPHONIC ACIDS, SULPHURIC ANHYDRIDE AND PHOSPHOROUS ANHYDRIDE, AND (2) AT LEAST ONE NON-METALLIC NITROGEN-CONTAINING ORGANIC COMPOUND BASIC WITH RESPECT TO THE ACIDIC AGENT IN THE SOLUTION, SELECTED FROM THE CLASS WHICH CONSISTS OF UREA, BIURET, FORMAMIDE, ACETAMIDE, ETHYLUREA, DIBUTYL-UREA, HYDROXYETHYL-UREA, DICYANDIAMIDE, CYANOACETAMIDE, GUANIDINE, GUANYL UREA AND BIGUANIDE, THE AMOUNT OF SOLIDS APPLIED RANGING FROM 8% TO 110% BY WEIGHT OF THE PULP IN THE DRY STATE, AND THE RATIO OF ACIDIC AND BASIC CONSTITUENTS IN SAID SOLUTION BEING SUCH AS TO YIELD A PRODUCT WHICH, AFTER THE BAKING TO BE HEREINAFTER DEFINED, HAS A PH OF FROM 2 TO PH TO 7 PH AS DETERMINED BY INDICATOR SOLUTIONS, AND CONTAINS AN AMOUNT OF COMBINED BASE ELEMENT OF THE ACID WHICH IS THE EFFECTIVE EQUIVALENT OF FROM 1/2 TO 6% OF PHOSPHOROUS, AND AN AMOUNT OF COMBINED NITROGEN FROM 4% TO 0.25% BY WEIGHT THEREAFTER DRYING THE FIBERS; SUBSEQUENTLY REACTING THE ACIDIC CONSTITUENT, THE NITROGENOUS BASIC CONSTITUENT AND THE CELLULOSE BY BAKING THE FIBERS AT TEMPERATURES BETWEEN 250* F. AND 400* F. FOR A TIME RANGING FROM 180 MINUTES AT THE LOWER TEMPERATURE TO 1 MINUTE AT THE HIGHER TEMPERTURE SO AS TO PRODUCE A COMPLEX CONTAINING THE ACID, CELLULOSE AND NITROGEN; AND SUBSEQUENTLY IMMERSING THE BAKED FIBERS, STILL IN COMPACTED FORM, IN HOT WATER, WHEREBY TO EFFECT RAPID AND SUBSTANTIALLY COMPLETE DISPERSION OF THE FIBROUS MATERIAL THROUGH THE BODY OF WATER. 